The present invention relates to an image forming apparatus such as a copier or printer, or a sheet processing device such as a sorter or a finisher, which is disposed in the image forming device, and especially relates to a sheet processing device in which, apart from stacking means such as a stacking part on which sheets can be stacked, support means such as a sheet holding part for being capable of temporarily holding the sheet supplied from image forming means is disposed on an upperstream side than the stacking means.
Conventionally, there has been known an image forming apparatus, a sorter, a finisher or the like which is provided with a sheet holding part wherein when a plurality of sheets is stacked and becomes a set of predetermined number of sheets, the set of sheets is processed, such as stapled or punch-holed, and then the set of sheets is rejected to the stack part.
Also, in this kind of the sheet holding part, at the time of temporarily staking sheets, the longer a stacking surface of the sheet toward the ejection direction is, the larger a size of the sheet can be stacked, and also this structure enables stable processing by preventing displacement of the set of the sheets when the set of the sheets is processed.
On the other hand, after processing the set of sheets, in order to facilitate ejecting the set of sheets from the sheet holding part to the stack part, the shorter the stacking surface of the sheet toward the ejection direction is, the easier ejection of the sheet to the stack part is.
Thus, as disclosed in U.S. Pat. No. 5,098,074 and in Japanese Patent Publication (KOKAI) No. 6-211414, it has been considered that an extension tray, which is extendable and retractable to the forward end of the ejection direction, is provided under the sheet holding part, and in the condition that the sheets are temporarily stacked on the sheet holding part, the extension tray is extended such that the tray is projected from the forward end in the ejection direction of the sheet holding part, so as to secure the stacking surface sufficiently; after the processing the sheets, the extension tray is retracted such that the tray is buried from the forward end part in the ejection direction of the sheet holding part so as to shorten the stacking surface.
However, since this freely extendable and retractable extension tray is simply extended or retracted, especially, in order to eject the processed sheets which are plurally stacked in a bundle (even not in case of stapling, sheets are in a bundle to eject at once) to the stack part, not only more ejecting force is required than ejecting sheet by sheet, but also an ejection roller for this ejection directly applies compulsive force only onto the uppermost sheet and the lowermost sheet in the set of sheets. Accordingly, it has been difficult to eject the set of processed sheets easily and orderly. Also, in the prior art disclosed in the aforementioned Patent Publications, balance between timing for placing into the stacking part and timing for retreating is not determined in consideration of orderliness.
Incidentally, in the sheet processing device structured as described above, there has been a problem that if a long sheet post-processing path is secured, the entire sheet processing device becomes large-sized.
Thus, it is considered to provide auxiliary support means for extending the sheet post-processing path in the downstream side of the sheet transferring direction. Sizes of the sheets in case of image forming are, however, not always the same, and for example, under the condition that a sheet of a B5 size is placed traversely longitudinal, in case the length of the sheet in the transferring direction is comparatively long, there is no deed to extend the sheet post-processing path.
As the sheet processing device, for example, there has been known the apparatus disclosed in the Japanese Patent Publication (KOKAI) No. 8-91686. This apparatus is structured that, in case of ejecting sheets stapled on the sheet holding part, a first motor is driven to lower a pinch roller such that the sheets are nipped between the pinch roller and an ejection roller, and subsequently a second motor is driven to rotate the ejection roller such that the sheets are nipped between the ejection roller and the pinch roller and ejected onto the stacking part.
However, in the above described sheet processing device, since driving for ascending and descending of the pinch roller and driving for rotating the ejection roller are operated by separate motors, the entire apparatus becomes large-sized. Also, driving by these motors has to be controlled by actuation of detecting means and actuator, which are disposed in the respective motors; accordingly, there was a possibility that a lag occurs between timing for nip operation and timing for ejecting operation due to dispersion in accuracy of the actuators.
An object of the invention is to provide a sheet processing device, wherein not only a stacking area of support means in a sheet holding part or the like can be variable, but also ejecting one or more sheets temporarily stacked to stacking means can be facilitated.
Another object of the invention is to achieve a sheet processing device with high reliability, wherein common driving means, which controls driving timing for at least the first ejecting means out of the first and second ejecting means and contacting-separating means or the like for contacting and separating the second ejecting means with respect to the first ejecting means, is provided so as to eliminate a timing lag.